Adaptive proportional control for determining interfaces of distinct materials

ABSTRACT

A process and apparatus for detecting changes in interface level between distinct materials within a container independent of any chemical or physical changes taking place within either or both of the distinct materials. Sensors are introduced into each of the materials and an additional sensor is placed across the interface, the output from each of the three sensors is transmitted to an adaptive detector device which combines these outputs by means of a control equation to give an emanating signal proportional solely to the position of the interface within the container.

9 O o a R g gm03-t72 0R 3 169511108 United States Patent 1151 3,695,108Wygant 1 51 Oct. 3, 1972 [54] ADAPTIVE PROPORTIONAL 3,111,031 11/1963Kuritza ..73/362 AR X CONTROL FOR DETERMINING 2,797,284 6/1957 Brooke...73/304 R X INTERFACES OF DISTINCT MATERIALS Primary Examiner-Louis R.Prince Assistant Examiner-Frederick Shoon [72] Inventor: Noel D. Wygant,Llttleton, Colo. Attorney ]oseph Herring, Richard C. wmson, JL

1 a and Jack L. Hummel |73| Assignee: Marathon Oil Company, Findlay,

Ohio [57] ABSTRACT 22 i J l 23, 1970 A process and apparatus fordetecting changes in interface level between distinct materials within acon- [21] Appl' 57,634 tainer independent of any chemical or physicalchanges taking place within either or both of the [52] US. Cl. ..73/290R, 73/290 v, 73/292, distinct materials Sensors are intr uced into eachof 73/304 C, 73/304 R the materials and an additional sensor is placedacross [51] Int. Cl ..G0lf 23/22, GOlf 23/26 the interface, e Output romeach of the three sen- [58] Field of Search .73/290 R, 290 U, 292, 299,sors is transmitted to an adaptive detector device 73/301, 304 R, 304 Cwhich combines these outputs by means of a control equation to give anemanating signal proportional [56] References Cited solely to theposition of the interface within the container. UNITED STATES PATENTS2,867,120 1/1959 Schafer ..73/304 c v 3,003,355 8/1961 Wright ..73/2993,424,002 1/1969 Johnson 73/2995 l6 v ADAPTIVE Y 2 DETECTOR MATERIAL '1!I L 12 (MATERIAL 1 OUTPUT INTERmCE) SIGNAL 6 22 MATgRIAL L J PATENTED B3 I 7 3.695, 1 08 l ADAPTIVE MATERIAL T 2 DETECTOR I 1 MATERIAL 2 1 L a2 1 44 [2 MATERIAL 1 (MATERIAL 62 1'2 OUTPUT 2 4 INTERFACE) SIGNALMATERIAL FIG. 2

(9 ,2 I (ezizfie a 2 SUM (e l a il -e 2 mie ifie ll qb] DIVIDE (e 1 SUM35/ s 6 4 L4 IS A A 1 '2 1; +8 ece5 5 e4 4 2 e2 2 e4 w k 38 FIG. 3 44/NVENTO/? N D. WYGANT & ATTORNEY BACKGROUND OF THE INVENTION 1 Field ofthe Invention I This invention relates generally to the measurement ofinterfaces of materials in contact with each other and relates moreparticularly to a novel process and apparatus for measuring positionalchanges for the interface between the materials even when thecharacteristics of the individual materials are changing, i.e. thesystem adapts to the changing characteristics of the materials whileproviding a measurement which depends solely on the position of theinterface.

2. Description of the Prior Art Interface meters, detectors,transducers, and other systems have long been used extensively invarious measuring, control and alarm systems. In simplified form, thesedevices give an output proportional to interface position. A simpleexample is a float gauge in an oil tank which gives an output indicatingoil level. This output can be used for measuring, controlling anddetecting the interface position within an enclosure such as a tank.

However, the inherent characteristics of the interface materials oftenundergo changes with time, temperature, pressure, as well as otherenvironmental changes. When these phenomena occur, the devices oftenrequire recalibration or extensive modification for protection againstthe discrepancies which arise as a result of these changes. It isobvious that these devices have serious shortcomings, making themunsuitable or completely unsatisfactory for many applications.

The present invention is advantageous over the prior art in that itmeasures the interface position independent of chemical or physicalcharacteristics of the materials. Furthermore, increased accuracy,greater reliability, and greater simplicity as well as increasedsensitivity, resolution, and response are additional advantages.

SUMMARY OF THE INVENTION This invention comprises introducing sensorsinto the materials and across the interface of the materials to measurecharacteristics of the materials and interface. The output from thesensors is transmitted to an adaptive detector which through electroniccircuits or pneumatic means operates and adapts to provide an outputsignal which is responsive to a change in interface position between thematerials being measured.

The system is not only useful for detection of interface changes, but itmay also be readily adapted to an alarming system, e. g., an audioalarm, or the system can utilize the output signal from the adaptivedetector to trigger a control mechanism for remedying any adverse changein interface position. For instance, a system can be adapted to withdrawor add one of the liquids in a settling tank in which a solventextraction technique is being used to separate normally miscible fluids.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more clearlyunderstood by reference to the accompanying drawings in which:

FIG. 1 shows a sensor bridging the interface between two unlikematerials.

FIG. 2 depicts the three sensors immersed in two different materials.The sensors are connected to an adaptive detector.

FIG. 3 shows a block diagram of the adaptive detector operations used toassimilate the outputs from each of the sensors of FIG. 2 using theunique control of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 2, sensors 2, 4, and 6are positioned in material 8, material 10 and across material interface12, all disposed within container 22. Outputs from sensors 2, 4, and 6are transmitted to adaptive detector 14 via suitable transmitting means16, 18, and 20, respectively. Detector 14 adapts the signals from thesensors to give output signal 24 proportional only to the position ofinterface 12 in container 22.

Linear output characteristics describe the sensors utilized. Therefore,the sensors produce an output proportional to the property of thematerial (in which it is immersed) and the length of the sensor. Theproperty of the material can be the dielectric constant, resistivity,temperature, velocity of sound, density, etc.

Examples of sensors for a given property are platinum thermometer fortemperature, transmitterreceiver system for velocity of sound, andpressure transducer for density.

For a two material system, see FIG. 1, these properties can be describedby the general equation:

0 l 1 2 2 I 1* 2 For our system, using materials 8 and 10 and sensor 2,see FIG. 2:

2 is the output of sensor 2 e is the output per unit length of sensor 2in material 8 e is the output per unit length of sensor 2 in material l0I is the length of sensor 2 in material 8 1' is the length of sensor 2in material 10 L is the length of sensor 2 General equation 1 alsoextends to the output of sensors 4 and 6, where the output of sensor 4is equal to 2 1., and the output of sensor 6 is equal to 2 1 Many typesof sensors or transducers are known to have the above linear outputcharacteristics. The outputs can be voltage, current, pressure, etc. Anexample is a coaxial capacitance sensor. Other types of sensors havingthis linear relationship, which are obvious to those skilled in the art,are meant to be included within this invention. A preferred sensorutilizes a twin-lead probe transducer in combination with a time domainreflectomer, (TDR), e.g., Model No. 1415A, Hewlett Packard Company.

Time domain reflectometry *Time Domain Reflectomery, Application Note62, Hewlett-Packard Co., 1964, 1501 Page Mill Road, Palo Alto, Calif, U.S. A. consists essentially of transmitting a very fast step func tioninto a transmission system, e.g., sensors 2, 4, and 6 which aretwin-lead probe transducers. The occurrence of an interface of twoliquids will be treated by the Time Domain Reflectometer as adiscontinuity, explainable under Transmission Theory as an abrupt changein an otherwise constant impedance of the transmission system.

The output of the TDR is a signal directly proportional to theimpedance. This signal is also directly proportional to the dielectricconstant of the material the probe is disposed in and the length of theprobe, i.e., the output follows the general equation :2 e l, e 1

The output signals from each of the three sensors are transmitted alonglines l6, l8 and 20 and are received and assimilated by adaptivedetector 14.

The container may be any suitable vessel capable of containing thematerials. Input and output valves may be positioned advantageously toallow injection or withdrawal of additional materials. These valves maybe automatically controlled to position desired interfaces. Thematerials themselves may be slightly miscible although preferablyimmiscible. Examples of materials which may form an interface includetwo liquid materials, e.g. oil and water, a gas and a liquid, e.g. waterand steam in equilibrium, a solid and a liquid, e.g. a supersaturatedbrine solution, two solids, e.g. wheat and barley contained within anagricultural storage bin, etc. It should be understood that while thedrawing depicts a two material interface system, the invention may beextended to include systems containing a plurality of materials, whereinterfaces exist between adjacent materials.

Referring to FIG. 3, while the summing and dividing networks shown inthe Figure will be described in terms of electronic circuitry, where theinputs e and e represent voltages, the operations shown in this Figuremay be accomplished by using current, pressure (hydraulic), pneumaticpressure, etc. as a means of arriving at the output e emanating fromsumming network, also called a summing circuit 30. The design and use ofelectronic summing circuits is well known in the art, and thistechnology may be used in the present invention.

The negative of the output from sensor 4 arriving via conductor 18 issummed in summing circuit 24 with the output from sensor 2 measuringacross the interface and fed to summing circuit 24 via line 20. Manualor automatic input 42 is fed to summing network 24 to scale 2 1 e 1 ande e e' l' and insure that the inputs are within the limits of operationof the network. The output from summing circuit 24 is equivalent to e 1e' l' e 1. and is transmitted via conductor 32 to dividing circuit 28.The output from conductor 18 is also transmitted to summing circuit 26and its negative is summed with the output from sensor 6 transmitted vialine 16. A span adjust coefficient equal to 1 over A via input 40 isapplied to summing circuit 26 to give an output equivalent to e 1 e 1all divided by A which is transmitted via conductor 34 to dividingcircuit 28. Any suitable DC voltage or DC current span may be used, suchas a span of :1, e.g., 4-20 milliamperes,

l5 volts DC, -50 milliamperes. In dividing circuit 28, the output fromsumming circuit 24 is divided by the output from summing circuit 26which gives a resultant output of:

This output is conveyed via conductor 36 to final summing circuit whereit is combined with offset term B conducted via 38 to give final outpute Offset term B represents the threshold value of the span, e.g., thespan of 1-5 volts, B 1 volt. Each of the adjusting input ofiset term Bvia 38, span A input 40, and scaling factor 42 may be manually orautomatically provided in each of the summing circuits.

In the operation of the invention, briefly, each of the sensors aredisposed in their respective materials and the interface sensor isdisposed through the interface or juncture of the materials. The outputof each of the three sensors is fed to adaptive detector 14. The outpute or 44 of adaptive detector 14 is a signal proportional to theinterface position and is independent of material characteristics.

The control equation of FIG. 3 is:

EXAMPLE 1 Basis: l =l =L 2; l =l =L =L. e e e, e (all sensors samematerial and length) This is the case where the sensor for detecting theinterface is one-half covered. Thus from the control equation, see FIG.3, the following:

The output is thus one half of the span term, plus the offset term, andis independent of e and e Obviously, a detection in interface changewill occur when the value of e deviates from this value of 'A/ 2 B.

EXAMPLE 2 In this case, ['2 0 and 1 L Z =16 L, that is, t 1 9;fqtfistssinathghtq aq is covers? only in material 8. Also, c Then: v

The output is again independent of the sensor output e, and e per unitof length of sensor. In this case the sensor is covered only in material8.

As actual examples, given A, a voltage span of 1-5 volts DC, case 1 willresult in an output a equal to 4 2 plus I 3 volts which is midpointbetween the span of 1-5 volts. In case 2, e =B 1 volt.

A reading of the foregoing application will make it obvious that thereare certain modifications and variations of the invention and these aremeant to be included within the reading of the specification and withinthe scope of the appended claims. All those skilled in the art willappreciate such variations and modifications.

. What is claimed is:

l. A process for detecting change in position of an interface defined bytwo adjacent different materials in a container comprising: i

a. introducing a first sensor of a certain length into the firstmaterial, the-sensor having an electrical output proportional to thesensed property of the material and the length of the sensor; the outputis transmitted to an adaptive detector,

b. introducing a second sensor of a certain length into the secondmaterial, the second sensor having an electrical output proportional tothe sensed property of the material and the length of the sensor; theoutput is transmitted to the adaptive detector,

c. introducing a third sensor of a certain length into the region of theinterface so that portions of the third sensor are in each of the twomaterials, the electrical output of the third sensor is proportional tothe product of the length of the third sensor in the first materialandthe sensed property of the first'material in summation with the productof the length of the third sensorin the second material and the sensedproperty of the second material;

the output of the third sensor is transmitted to the adaptive detector,combining each of the sensor outputs in the adaptive detector inaccordance with the formula:

10. The process of claim 1 wherein the output of the first sensor is lethe output of the second sensor is Ie and the output of the third sensoris e 1 e l' where e, is the output per unit length of the first sensorin the first material e is the output per unit length of the secondsensor in the second material er is the output per unit length of theportion of the third sensor in the first material e':, is the output perunit length of the portion of the third sensor in the second material Iis the length of sensors one and two 1 is the length of the portion ofthe third sensor in the first material 1' is the length of the portionof the third sensor in the second material and where the operations onthe individual outputs are combined within the adaptive detector inaccordance with the following relation to give the total output eindicative of the interface level:

where A represents the span of the output of each sensor proportional tothe length l, and B represents an offset term equivalent to the lowestpossible output value from which span A is measured.

11. The process of claim 10 wherein the three sensors are the samelength.

12. The process of claim 10 wherein the three sensors are coaxialcapacitance sensors.

13. The process of claim 10 wherein the sensors are twin-lead probesensors.

' 14. An apparatus for determining interface change between adjacentmaterials comprising:

a container containing the adjacent materials whose points of contactdefine an interface between the materials;

' a first sensor disposed within one of the adjacent e ials;

output from the third sensor-output from the first sensor (output fromthe second sensor outputfrornthe firsteenyr) 6. The process of claim 5wherein the impedance of each sensor is dependent on the length of eachsensor and the dielectric constant of the material in which each sensoris disposed.

7. The process of claim 1 wherein the sensed property is the dielectricconstant of the material.

8. The process of claim 1 wherein the sensed property is the resistivityof the material.

9. The process of claim 1 wherein the sensed property is the temperatureof the material.

a second sensor disposed within the other adjacent material;

a third sensor disposed within both adjacent materials and spanning theinterface;

means for transmitting to an adaptive detector an output signal from thefirst sensor proportional to the length of the first sensor and thesensed property of the material in contact with the first sensor;

means for transmitting to the adaptive detector an output signal fromthe second sensor proportional to the length of the second sensor andthe sensed property of the material in contact with the second sensor;

means for transmitting to the adaptive detector an output signal fromthe third sensor proportional to the portions of the length of the thirdsensor and the sensed property of the first and second materials incontact with the respective portions;

the adaptive detector combining each of the sensor outputs in accordancewith the formula:

output from the third sensor-output from the first sensor wherein e, isthe combined output, A is a constant proportional to the span of eachoutput, and B represents (output from the second sensor-output frorn thefirst sensor d. combining each of the sensor outputs in the adaptivedetector in accordance with the formula:

output from the third sensor-output from the first sensor an offset termequivalent to the lowest output value from which span A is measured.

1 5. The apparatus of claim 14 wherein the sensed property is thedielectric constant of the material.

16. A process for detecting change in position of an interface definedby two adjacent different materials in a container comprising:

a. introducing a first sensor of a certain length into the firstmaterial, the sensor having an electrical output proportional to thevelocity of sound of the material and the length of the sensor; theoutput is transmitted to an adaptive detector,

b. introducing a second sensor of a certain length into the secondmaterial, the second sensor having an electrical output proportional tothe velocity of sound of the material and the length of the sensor; theoutput is transmitted to the adaptive detector,

first material in summation with the product of the wherein e, is theoutput of the adaptive detector, A is a constant proportional to thespan of each sensor output, and B represents an offset term equivalentto the lowest output value from which the span A is measured.

17. A process for detecting change in position of an interface definedby two adjacent different materials in a container comprising:

a. introducing a first sensor of a certain length into the firstmaterial, the sensor having an electrical output proportional to thedensity of the material and the length of the sensor; the output istransmitted to an adaptive detector,

b. introducing a second sensor of a certain length into the secondmaterial, the second sensor having an electrical output proportional tothe density of the material and the length of the sensor; the output istransmitted to the adaptive detector,

. introducing a third sensor of a certain length into the region of theinterface so that portions of the third sensor are in each of the twomaterials, the electrical output of the third sensor is proportional tothe product of the length of the third sensor in the first material andthe density of the first material in summation with the product of thelength of the third sensor in the second material and the density of thesecond material; the output of the third sensor is transmitted to theadaptive detector,

d. combining each of the sensor outputs in the adaptive detector inaccordance with the formula:

output from the third-,sensor-output from the first sensor (o u tputfrom the seeondl'sensor output from the firstsensor) length of the thirdsensor in the second material and the velocity of sound of the secondmaterial;

the output of the third sensor is transmitted to the adaptive detector,

P0-105O I UNITED STATES PATENT OFFICE 5/ 69) CERTIFICATE OF CORRECTIONPatent NO 3,695,108 Dated October 3, 1972 Inventor(s) Noel Wygant It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby cbrrected as shown below:

Col. 3, line 50: Delete "e e and insert Col. 5, line 3: After "4" insertr Col. 5, line 5: Delete "32," and insert --l.

Col. 6, line 24: Delete "3" and insert (subscript) Signed and sealedthis 6th clay of February 1973.

(SEAL) Attest:

EDWARD M. FLETCH ER,JR. ROBERT GOTTSCHA'LK Arresting OfficerCommissioner OfPatents-

1. A process for detecting change in position of an interface defined bytwo adjacent different materials in a container comprising: a.introducing a first sensor of a certain length into the first material,the sensor having an electrical output proportional to the sensedproperty of the material and the length of the sensor; the output istransmitted to an adaptive detector, b. introducing a second sensor of acertain length into the second material, the seCond sensor having anelectrical output proportional to the sensed property of the materialand the length of the sensor; the output is transmitted to the adaptivedetector, c. introducing a third sensor of a certain length into theregion of the interface so that portions of the third sensor are in eachof the two materials, the electrical output of the third sensor isproportional to the product of the length of the third sensor in thefirst material and the sensed property of the first material insummation with the product of the length of the third sensor in thesecond material and the sensed property of the second material; theoutput of the third sensor is transmitted to the adaptive detector, d.combining each of the sensor outputs in the adaptive detector inaccordance with the formula: wherein ec is the output of the adaptivedetector and A is a constant proportional to the span of each sensoroutput.
 2. The process of claim 1 wherein the two materials are fluids.3. The process of claim 2 wherein one material is substantially in thegaseous phase and the other material is substantially in the liquidphase.
 4. The process of claim 1 wherein the two materials are liquids.5. The process of claim 1 wherein the outputs are electric signals froma time domain reflectometer, which outputs are proportional to theimpedance of the sensors.
 6. The process of claim 5 wherein theimpedance of each sensor is dependent on the length of each sensor andthe dielectric constant of the material in which each sensor isdisposed.
 7. The process of claim 1 wherein the sensed property is thedielectric constant of the material.
 8. The process of claim 1 whereinthe sensed property is the resistivity of the material.
 9. The processof claim 1 wherein the sensed property is the temperature of thematerial.
 10. The process of claim 1 wherein the output of the firstsensor is le1, the output of the second sensor is le2 and the output ofthe third sensor is e3l3 + e'' 3l'' 3 where e1 is the output per unitlength of the first sensor in the first material e2 is the output perunit length of the second sensor in the second material e3 is the outputper unit length of the portion of the third sensor in the first materiale'' 3 is the output per unit length of the portion of the third sensorin the second material l is the length of sensors one and two l3 is thelength of the portion of the third sensor in the first material l'' 3 isthe length of the portion of the third sensor in the second material andwhere the operations on the individual outputs are combined within theadaptive detector in accordance with the following relation to give thetotal output ec indicative of the interface level: ec A/l(e2 - e1)(e3l3 + e'' 3l'' 3 - e1l) + B where A represents the span of the outputof each sensor proportional to the length l, and B represents an offsetterm equivalent to the lowest possible output value from which span A ismeasured.
 11. The process of claim 10 wherein the three sensors are thesame length.
 12. The process of claim 10 wherein the three sensors arecoaxial capacitance sensors.
 13. The process of claim 10 wherein thesensors are twin-lead probe sensors.
 14. An apparatus for determininginterface change between adjacent materials comprising: a containercontaining the adjacent materials whose points of contact define aninterface between the materials; a first sensor disposed within one ofthe adjacent materials; a second sensor disposed within the otheradjacent material; a third sensor disposed within both aDjacentmaterials and spanning the interface; means for transmitting to anadaptive detector an output signal from the first sensor proportional tothe length of the first sensor and the sensed property of the materialin contact with the first sensor; means for transmitting to the adaptivedetector an output signal from the second sensor proportional to thelength of the second sensor and the sensed property of the material incontact with the second sensor; means for transmitting to the adaptivedetector an output signal from the third sensor proportional to theportions of the length of the third sensor and the sensed property ofthe first and second materials in contact with the respective portions;the adaptive detector combining each of the sensor outputs in accordancewith the formula: wherein ec is the combined output, A is a constantproportional to the span of each output, and B represents an offset termequivalent to the lowest output value from which span A is measured. 15.The apparatus of claim 14 wherein the sensed property is the dielectricconstant of the material.
 16. A process for detecting change in positionof an interface defined by two adjacent different materials in acontainer comprising: a. introducing a first sensor of a certain lengthinto the first material, the sensor having an electrical outputproportional to the velocity of sound of the material and the length ofthe sensor; the output is transmitted to an adaptive detector, b.introducing a second sensor of a certain length into the secondmaterial, the second sensor having an electrical output proportional tothe velocity of sound of the material and the length of the sensor; theoutput is transmitted to the adaptive detector, c. introducing a thirdsensor of a certain length into the region of the interface so thatportions of the third sensor are in each of the two materials, theelectrical output of the third sensor is proportional to the product ofthe length of the third sensor in the first material and the velocity ofsound of the first material in summation with the product of the lengthof the third sensor in the second material and the velocity of sound ofthe second material; the output of the third sensor is transmitted tothe adaptive detector, d. combining each of the sensor outputs in theadaptive detector in accordance with the formula: wherein ec is theoutput of the adaptive detector, A is a constant proportional to thespan of each sensor output, and B represents an offset term equivalentto the lowest output value from which the span A is measured.
 17. Aprocess for detecting change in position of an interface defined by twoadjacent different materials in a container comprising: a. introducing afirst sensor of a certain length into the first material, the sensorhaving an electrical output proportional to the density of the materialand the length of the sensor; the output is transmitted to an adaptivedetector, b. introducing a second sensor of a certain length into thesecond material, the second sensor having an electrical outputproportional to the density of the material and the length of thesensor; the output is transmitted to the adaptive detector, c.introducing a third sensor of a certain length into the region of theinterface so that portions of the third sensor are in each of the twomaterials, the electrical output of the third sensor is proportional tothe product of the length of the third sensor in the first material andthe density of the first material in summation with the product of thelength of the third sensor in the second material and the density of thesecond material; the output of the third sensor is transmitted to theadaptive detector, d. combining each of the sensor outputs in theadaptive detector in accordance with the formula: wherein ec is theoutput of the adaptive detector and A is a constant proportional to thespan of each sensor output.